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Until now, there were many strange things already about Venus. Now, there is one more, with possible climate implications. From ESA’s Venus Express: Could Venus be shifting gear?

[…] ESA’s Venus Express spacecraft has discovered that our cloud-covered neighbour spins a little slower than previously measured. […] Over its four-year mission, Magellan was able to watch features rotate under the spacecraft, allowing scientists to determine the length of the day on Venus as being equal to 243.0185 Earth days. . However, surface features seen by Venus Express some 16 years later could only be lined up with those observed by Magellan if the length of the Venus day is on average 6.5 minutes longer than Magellan measured. […]

A quick back-of-the-envelope calculation indicates that 6.5 minutes in 16 years translates in 1.56 watt per hour on each square meter of Venus’ surface, if all the rotational energy is converted into heat (I couldn’t double-check the results though). If this process is cumulative, it will certainly have huge consequences.

Venus’ retrograde rotation, incredibly massive atmosphere and relatively young (<500 million years) surface will be elegantly explained by the crash of a massive satellite half a billion years ago (with subsequent melting of much if not the whole crust, and humongous outgassing).

Current lead-melting surface temperatures will be just as beautifully explained by simple adiabatic processes.

The role of CO2 in the heating of the atmosphere via some “greenhouse effect” will be seriously reconsidered and almost completely dismissed.

The next time a warmist yells Venus. Just yell back Mars. Its’ atmosphere is 95% carbon dioxide and yet, oops – it’s not 400 degrees, instead, it’s minus 40. The warmists with half a brain might come back at you with the explanation that Mars’s atmosphere is thin, but that’s just fine. That IS the point really isn’t it? Mars is cold because it’s atmosphere is so thin, and for exactly the opposite reason, that’s why Venus is Hot.

Big news today about Mars’ peculiar north-south terrain divide having been caused by the impact of a Moon-size object shortly after the planet formed. Since there is also strong evidence for Earth having undergone a similar impact, with a Mars-size planetoid, thereby forming our Moon, it would be odd to imagine that no such catastrophe ever occurred to Venus.

After all there’s lots still to explain about “Earth’s Twin”: a very slow retrograde rotation, an incredibly massive atmosphere and a relatively young (<500 million years) surface. To me, the whole setting cries out loud for an “impact” explanation, rather than the classic “it’s warm because of the CO2!” theory that says nothing about all the other peculiarities (and it’s not exactly necessary…).

Ok n-g I presume we can now do assuming all niceties instead of repeating our thanks 😎 so let’s try to clarify a few points.

To my mind, they act very differently

the rest of my question was “Wouldn’t moist convection for example drastically change the consequences of an increase in atmospheric CO2?”.

And the point was: when people say, look at Venus to see what GHG warming can do, the scientific answer should be that no comparison can be done with Earth as the whole mechanism of “warming” is very different (whatever CO2 may or may not be doing…if only because we have so much water vapor).

May I dare say we agree on this point?

When you’re looking at the planetary energy balance, the single number albedo is not just the starting point, but also the ending point

But surely an atmosphere, say, with low albedo in UV and high albedo to visible and IR does not behave as an atmosphere that is the other way around?

Earth’s for example is able to keep a bit warmer by the presence of UV-absorbing ozone in the stratosphere. That would mean a lower albedo in UV than in visible light, wouldn’t it?

The dry adiabatic lapse rate depends only on gravity and heat capacity

If the greenhouse effect is so strong on Venus, why isn’t the lapse rate much larger, and much larger than Earth’s, given the fact that the amount of CO2 decreases a lot between the surface and the height of 60km?

Surely the lower one gets, the more GHG there are, the higher the ability to trap heat.

Suppose there were no greenhouse effect on Venus

As you say, this is an argument, not proof

The fact that the IR emissions from Venus come from the atmosphere and not from the surface constitutes the proof

The fact that visible light comes from the atmosphere and not from the surface only proves there’s lots (lots!) of clouds on Venus. Why would the same observation regarding IR mean something else?

If the atmosphere of Earth were 100 times more massive

Let’s imagine Earth had a 10-km deep, reasonably large crater in the middle of a continent, with no liquid water on its bottom at all. What would be the temperature at the bottom of the crater? With a lapse rate for saturated air of 5.46K/km, 288+5.46*10=342K or 70C. Right? Wrong?

Let’s compute (in a simplified manner!) what would happen were Earth suddenly equipped with an atmosphere as massive as Venus’ (ie 90 times more than ours).

Given the similarities in mass and diameter of the two planets, we can assume this new atmosphere would behave similarly to Venus’, and in particular, purely adiabatically below 60km (instead of below 12km as at present).

For another simplification, let’s also imagine the new atmosphere to be just as our current one but without any water.

The lapse rate for dry Earth atmosphere is known and is 9.760 K/km.

How higher would the surface temperature be, with a dry atmosphere and a 60-km-thick troposphere?

9.760 * (60-12) = 468K higher than at present (288K)

The total for Earth is then 756K. Compare that to Venus’ surface temperature of 735K.

For an amazing coincidence, that’s 97% of the above, whilst the ratio of absorbed Solar radiation at Venus compared to Earth is… 96%.

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Note how the increase in temperature doesn’t depend on any greenhouse gas.

And so do we really need to believe in greenhouse warming when mere mass can explain the observations?